1. Field of the Invention
The invention relates to a multiple gear transmission for a bicycle with an input shaft and an output shaft supported in a transmission housing, whereby the input shaft is embodied to receive pedal cranks and both ends of the input shaft protrude from the transmission housing, and one of the ends of the output shaft protrudes from the transmission housing and the output shaft is embodied at this end to receive a drive sprocket.
2. Discussion of Background Information
A transmission of this type is known, e.g., from U.S. Pat. No. 5,553,510. Gear wheels are arranged on both shafts, which gear wheels can be respectively connected to the respective shaft in a torque-proof manner via a freewheel. Pivotable connector sprockets are provided for shifting the transmission, which sprockets can mesh respectively with two gear wheels lying opposite. A transmission of this type is not only designed in a very complex manner in terms of construction, but it is also very susceptible to faults, since it is not ensured that the gear wheels are stationary when the clutch wheel is engaged. Loud shifting noises are inevitable.
In the past forty years the chain drive with a shifting capability at the rear axle has become widely used with bicycles. To this end, a rotatable bottom bracket with one or more chain rings is mounted onto the frame which forms the load-bearing component of the bicycle with all its receiving points for the front wheel fork, the seat post and the rear wheel. A cassette comprising up to ten sprockets of different sizes is located on the hub of the rear wheel. At one drop-out located directly at the rear axle a rear derailleur is installed, which has the task of guiding the chain in the sprockets of the cassette and to render possible shifting processes. Through a derailer that is usually installed at the seat tube it is possible to switch between the various chain rings at the bottom bracket. The capability of shifting allows the rider to adapt the gear ratio of his/her drive to the respective riding situation. Bicycles with a shifting system as described above are generally referred to as bicycles with derailleur gears.
As the components are mounted outside on the frame for constructional reasons with a bicycle with derailleur gears, the components are particularly strongly exposed to environmental influences. Dirt and water thus come into contact with rear derailleur, chain, cassette and other components in an unobstructed manner. This drastically reduces the efficiency of derailleur gears, which is initially very good, so that a considerable part of the force must be used to overcome the resistances within the shifting system. In order to ensure functionality it is necessary to regularly service the components of the derailleur gears, which includes cleaning and greasing the components and adjusting them precisely. This adjustment can easily change, e.g., with falls or contact with objects (stones, branches, etc.). As tiny dirt particles always remain in the shifting system and in particular in the bearings even with the most intensive servicing, some parts need to be replaced regularly. In particular the parts susceptible to wear, such as chain rings and chain require an annual replacement, which in turn incurs additional expenses. Furthermore, components can be damaged or torn off the frame with a fall or contact with stones or branches.
Alternatively to the “derailleur gears” the so-called “integral rear hub” was developed, in which the shifting processes take place in a transmission in the rear wheel hub. The parts required with the derailleur gears; rear derailleur, derailer and cassette are thus omitted. Bicycles of this type are generally called bicycles with integral rear hub. An integral rear hub thus avoids the disadvantages of derailleur gears. Because of the transmission integrated into the rear wheel hub, however, the weight of the rear wheel increases. In particular with so-called mountain bikes, which are moved off-road, an increase in mass at the rear wheel becomes highly noticeable. This applies in particular to bicycles with rear wheel suspension. The ratio of sprung to unsprung mass is of decisive importance for the riding behavior of a sprung wheel. The larger the unsprung mass is in relation to the sprung mass, the more critical is the riding behavior of the wheel. With high unsprung mass (heavy rear wheel) thrusts caused by road bumps cannot be compensated for in an optimum manner by the chassis.
With a known bicycle (cf. DE 103 39 207) the transmission is located within the bicycle frame. The bottom bracket shell of the classic bicycle frame is omitted and replaced by a transmission housing. This is a joint housing for transmission and bottom bracket. Similar to the bicycles with transmission hub, the power is transmitted to the rear wheel via a chain or a toothed belt, the chain and the rear wheel hub do not have a shifting function with this system. The rear wheel hub can thus be built in a very light manner, which results in a more efficient rear wheel suspension. Furthermore, the center of gravity shifts to the center of the wheel, directly below the rider, which results in a more agile and controlled riding behavior. In addition, the so-called “platform strategy” can be used with the aid of the transmission integrated into the frame. Whereas it has hitherto been customary in bicycle construction to first build a frame and then subsequently to equip it with its components, the concept of the transmission integrated into the frame renders it possible to use the platform strategy known from automobile construction in bicycle production. For example components, such as shifting system, suspension, the complete power transmission, but also brakes, generator and lighting are firmly installed in the transmission housing as a platform. The customer-specific parts, which complete the bicycle according to customer specification, are then mounted to the transmission thus equipped. The transmission comprises a planetary transmission and a primary drive. The primary drive is necessary because the planetary transmission developed for the use in a transmission hub does not withstand the high torques acting in the bottom bracket. The primary drive brings the planetary transmission to a higher rotational speed, so that it can withstand the acting forces. This construction, however, lowers the efficiency of the drive.
Based on these problems, the multiple gear transmission described at the outset is to be improved.